This invention relates to a NC machine tool having a constitution in which a table for placing a work thereon and a spindle for setting a tool are relatively moved by feed mechanisms to carry out machining.
In the conventional machine tool, a feed mechanism using a ball screw is general, by which a table or a spindle is moved.
With the recent progress of higher speed of a machine tool, it has been required to feed a table or a spindle at high speed.
For achieving the higher speed, a feed mechanism using a linear motor as a drive source has been produced by way of trial, but the sufficient result has not been obtained.
The conventional feed mechanism of a ball screw type is able to realize a highly accurate and smooth feeding. However, in the ball screw type, it has been difficult to correspond to the higher speed since a feed speed has a limitation.
It is an object of this invention to provide a NC machine tool capable of making a feed speed higher, and being provided with a feed mechanism enabling smooth and highly accurate feeding.
Solving means of the present invention are illustrated as follows:
(1) A NC machine tool having a constitution in which a table for placing a work thereon and a spindle for setting a tool are relatively moved by three feed mechanisms, for X-axis, for Y-axis, and for Z-axis, to carry out machining, wherein a preload is applied to all the three feed mechanisms, for X-axis, for Y-axis, and for Z-axis, using a rack-pinion, and using two motors for each axis to prevent backlash in the rack-pinion.
(2) A horizontally arranged rack has teeth directed downward.
(3) As a rack-pinion, a helical rack-pinion is used.
(4) As a rack-pinion, a double-helical rack-pinion is used.
In the NC machine tool according to the present invention, a table for placing a work thereon and a spindle for setting a tool are relatively moved by three feed mechanisms, for X-axis, for Y-axis, and for Z-axis, to carry out machining. In all the three feed mechanisms, for X-axis, for Y-axis, and for Z-axis, a rack-pinion is used.
Two motors are used for each axis to double the driving force, and backlash of a rack and a pinion is removed by preloading.
Moreover, a horizontally arranged rack has teeth directed downward or directed laterally. Thereby, it is possible to prevent the rack tooth face from staying of foreign matter thereon.
As a rack-pinion, a helical rack-pinion or a double-helical rack-pinion can be used. By using them, smoother feeding can be realized.